Carbon fiber bundle process for producing the same and thermoplastic resin composition and molded article thereof

ABSTRACT

A carbon fiber bundle is provided which can develop satisfactory interfacial adhesion to polyolefin-based resins, especially polypropylene resins. The carbon fiber bundle comprises a plurality of single fibers that was sized with a sizing agent comprising: a polymer having a main chain formed of carbon-carbon bonds, containing an acid group in at least part of side chains or at least a part of main chain ends, and representing an acid value of 23 to 120 mgKOH/g as measured in accordance with ASTM D1386; or a polymer having a main chain formed of carbon-carbon bonds and containing at least either of an epoxy group and an ester group in at least a part of side chains or at least a part of main chain ends.

TECHNICAL FIELD

The present invention relates to a carbon fiber bundle, and method forproducing the same, which can be used as a thermoplastic reinforcingmaterial. The present invention further relates to a thermoplastic resincomposition, and molded article thereof, which uses such a carbon fiberbundle.

BACKGROUND ART

A carbon fiber bundle is a form gathering together a plurality singlefibers consisting of carbon, and is used as a reinforcing material forthermoplastic resins or the like.

When used as a reinforcing material for thermoplastic resins, carbonfiber bundles are usually supplied being a form cut into lengths of 5 to15 mm. During production of pellets obtained by kneading this carbonfiber bundles and a thermoplastic resin, it is necessary to supply thecarbon fiber bundles in a fixed quantity into an extruder. In order todo this, the form stability of the carbon fiber bundles is important. Aform that is not suitable can become a cause for discharge unevenness.Also, because a fixed extrusion rate cannot be attained, strand breakageoccurs, whereby there is the risk of pellet productivity dramaticallyfalling.

Materials known as long-fiber pellets are also attracting attention, inwhich carbon fiber bundles having a continuous fiber form are charged inthe pellet production process. During this process, fluff or fly iseasily formed on the carbon fiber bundle, or, the bundle is easilyloosened, so that the handling is difficult.

Carbon fiber bundles can also be formed into a fabric and used as asheet material impregnated with a thermoplastic resin, wherein theweaving quality of the carbon fiber bundles, the handleability of thecloth after being woven and the like are important properties.

For reasons as described above, to improve carbon fiber bundlehandleability and the physical properties of a material into whichcarbon fiber bundles have been blended, it is conventional to use carbonfiber bundles which have been converged by a sizing treatment whichdeposits, for example, about 2 to 5 wt % of a sizing agent that iscompatible with the matrix resin, such as an agent having an epoxy resinas a main component.

Examples of the thermoplastic resin used as the matrix resin typicallyinclude polycarbonate resin, nylon resin, polyester resin and the like.Recently, however, the number of cases of using a polyolefin-based resinhas been increasing for reasons of recyclability and cost. Polypropyleneresin in particular has been drawing attention in recent years.

Since polyolefin-based resins are basically nonpolar, their interfacialadhesion with the carbon fibers or glass fibers is extremely poor andthe effects of improved mechanical properties as a reinforcing materialcannot be adequately expressed in many cases. Countermeasures for thisare known to include a method which improves adhesion by adding an acidmodified polyolefin-based resin to the matrix resin, and a method whichsubjects the carbon fibers or glass fibers to a sizing treatment with asizing agent constituted from a polyolefin-based resin and a silanecoupling agent and the like. Another known method, as described inJapanese Patent Application Laid-Open No. 6-107442 (Patent Document 1),subjects the carbon fibers or glass fibers to a sizing treatment using asizing agent having acid modified polypropylene as an essentialcomponent.

However, in the method which adds an acid modified polyolefin-basedresin to the matrix resin, a large amount of acid modifiedpolyolefin-based resin has to be added, whereby a product havingexcellent recyclability and cost effectiveness cannot be obtained. Onthe other hand, in the method sizing with a sizing agent containing asilane coupling agent, because carbon fibers do not have so many oxygengroups on the surface as compared with glass fibers, the effects forimproving interfacial adhesion are rather minimal.

Further, although the method sizing with a sizing agent having acidmodified polypropylene as an essential component described in PatentDocument 1 achieves good interfacial adhesion as compared with apolyolefin-based resin, in the case of carbon fibers the effects werenot sufficient.

Patent Document 1: Japanese Patent Application Laid-Open No. 6-107442

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention was created in view of the above-describedmatters, wherein it is an object thereof to provide a carbon fiberbundle which can develop satisfactory interfacial adhesion with apolyolefin-based resin, especially polypropylene resin.

Means for Solving the Problems

The present invention includes:

a carbon fiber bundle comprising a plurality of single fibers, and sizedwith a sizing agent comprising:

a polymer having a main chain formed of carbon-carbon bonds, containingan acid group in at least a part of side chains or at least a part ofmain chain ends, and representing an acid value of 23 to 120 mgKOH/g asmeasured in accordance with ASTM D1386; or

a polymer having a main chain formed of carbon-carbon bonds, andcontaining at least either of an epoxy group and an ester group in atleast a part of side chains or at least a part of main chain ends. Thepresent invention especially includes the following embodiments:

(1) The carbon fiber bundle, wherein the sizing was conducted afterpre-sized with a pre-sizing agent consisting of an epoxy resin;

(2) The carbon fiber bundle, wherein the single fibers comprise aplurality of wrinkles on their surface, wherein a vertical differencebetween a highest portion and a lowest portion in a region defined by 2μm of circumferential length×1 μm of fiber axial direction length of thesingle fibers is 40 nm or more.

The method for producing the carbon fiber bundle of the above (1)especially includes the following embodiment:

A method for producing a carbon fiber bundle comprising a plurality ofsingle fibers, comprising the steps of:

pre-sizing the carbon fiber bundle with a pre-sizing agent consisting ofan epoxy resin;

sizing the pre-sized carbon fiber bundle, so that an amount of a sizingagent to the total is 1 to 5 wt %, by using an aqueous sizing agentsolution dissolving or dispersing in water the sizing agent comprising:

a polymer having a main chain formed of carbon-carbon bonds, containingan acid group in at least a part of side chains or at least a part ofmain chain ends, and representing an acid value of 23 to 120 mgKOH/g asmeasured in accordance with ASTM D1386; or

a polymer having a main chain formed of carbon-carbon bonds, containingat least either of an epoxy group and an ester group in at least a partof side chains or at least a part of main chain ends;

cutting the carbon fiber bundle to a prescribed length; and

drying the carbon fiber bundle cut to the prescribed length.

The method for producing the carbon fiber bundle of the above (2)especially includes the following preferable embodiment:

A method for producing a carbon fiber bundle comprising a plurality ofsingle fibers, wherein the single fibers comprise a plurality ofwrinkles on their surface, wherein a vertical difference between ahighest portion and a lowest portion in a region defined by 2 μm ofcircumferential length×1 μm of fiber axial direction length of thesingle fibers is 40 nm or more, comprising the steps of:

sizing the carbon fiber bundle, so that an amount of a sizing agent tothe total is 1 to 5 wt %, by using an aqueous sizing agent solutiondissolving or dispersing in water the sizing agent comprising:

a polymer having a main chain formed of carbon-carbon bonds, containingan acid group in at least a part of side chains or at least a part ofmain chain ends, and representing an acid value of 23 to 120 mgKOH/g asmeasured in accordance with ASTM D1386; or

a polymer having a main chain formed of carbon-carbon bonds, containingat least either of an epoxy group and an ester group in at least a partof side chains or at least a part of main chain ends;

cutting the carbon fiber bundle to a prescribed length with regulatingthe moisture content of the carbon fiber bundle to 20 to 60 wt %; and

drying the carbon fiber bundle cut to a prescribed length.

In addition, the present invention includes a thermoplastic resincomposition comprising a thermoplastic resin and the carbon fiberbundle, wherein the carbon fiber bundle content is 3 to 60 wt %.

Further, the present invention includes a molded article obtained bymolding the thermoplastic resin composition.

Effects of the Invention

According to the carbon fiber bundle of the present invention,satisfactory interfacial adhesion with polyolefin-based resins,especially polypropylene resin, can be developed.

BEST MODE FOR CARRYING OUT THE INVENTION

The carbon fiber bundle according to the present invention is a carbonfiber bundle comprising a plurality of single fibers, and sized with asizing agent comprising:

a polymer having a main chain formed of carbon-carbon bonds, containingan acid group in at least a part of side chains or at least a part ofmain chain ends, and representing an acid value of 23 to 120 mgKOH/g asmeasured in accordance with ASTM D1386; or

a polymer having a main chain formed of carbon-carbon bonds, andcontaining at least either of an epoxy group and an ester group in atleast a part of side chains or at least a part of main chain ends.Especially, following preferable embodiments are provided:

(1) The carbon fiber bundle, wherein the sizing was conducted afterpre-sized with a pre-sizing agent consisting of an epoxy resin;

(2) The carbon fiber bundle, wherein the single fibers comprise aplurality of wrinkles on their surface, wherein a vertical differencebetween a highest portion and a lowest portion in a region defined by 2μm of circumferential length×1 μm of fiber axial direction length of thesingle fibers is 40 nm or more.

(Carbon Fiber Bundle Before Sizing)

In the present invention there are no particular limits on the carbonfiber bundle before sizing, so that a carbon fiber bundle comprising aplurality of known single fibers can be employed. Normally, it is a formgathering together about 1,000 to 50,000 single fibers having an averagediameter of 5 to 8 μm. The single fibers constituting such a carbonfiber bundle are obtained by making an acrylonitrile polymer, pitchobtained from petroleum or coal, or the like into a fiber, and thencarbonizing the fiber. Fibers that can be used include those which haveundergone the carbonizing treatment, fibers which have undergone a wetelectrolytic oxidation treatment to thereby incorporate anoxygen-containing functional group onto the surface, and fibers whichhave bee pre-sized.

In particular, examples of a carbon fiber bundle before sizing which canbe preferably used in the present invention include:

(I-1) A carbon fiber bundle comprising a plurality of single fibers,wherein the single fibers comprise a plurality of wrinkles on theirsurface, wherein a vertical difference between a highest portion and alowest portion in a region defined by 2 μm of circumferential length×1μm of fiber axial direction length of the single fibers is 40 nm ormore; and

(I-2) A carbon fiber bundle pre-sized with a pre-sizing agent consistingof an epoxy resin.

In the present invention, the carbon fiber bundle preferably comprises aplurality of single fibers, wherein the single fibers comprise aplurality of wrinkles on their surface, wherein a vertical differencebetween a highest portion and a lowest portion in a region defined by 2μm of circumferential length×1 μm of fiber axial direction length of thesingle fibers is 40 nm or more (I-1). Further, the vertical differencebetween the highest portion and the lowest portion is preferably 10% orless of the diameter of the single fibers. The depth of the wrinkleswhich are present on the single fiber surface is defined by the verticaldifference between the highest portion and the lowest portion in theregion defined by 2 μm of circumferential length×1 μm of fiber axialdirection length. A wrinkle on the single fiber surface refers to anuneven shape having a length of 1 μm or more in a given direction. Thisdirection is not particularly limited, and may be parallel,perpendicular or at an angle to the fiber axial direction. In thegeneral production method for a carbon fiber bundle comprising aplurality of single fibers, wrinkles which are approximately parallel tothe fiber axial direction are present on the usual single fiber surface.The vertical difference can be estimated in the following manner basedon the surface shape obtained by scanning the surface of the singlefibers with a scanning atomic force microscope (AFM).

Several single fibers of a carbon fiber bundle are placed onto aspecimen stage, and fixed at both ends. Dotite is applied around theirperiphery to form measurement samples. Employing a cantilever made fromsilicon nitride, an atomic force microscope (Model: SPI 3700/SPA-300(trade name), manufactured by Seiko Instruments Inc.) is used to measurein AFM mode by repeatedly scanning a 2 to 7 μm range in the peripherydirection of the single fibers while slowly moving in 1 μm intervalsacross the fibers in a fiber axial direction. The low frequencycomponent of the obtained measured images is cut by two-dimensionalFourier transform, and the cut images then undergo an inverse transform.The vertical difference between the highest portion and the lowestportion in the region defined by 2 μm of circumferential length×1 μm offiber axial direction length is then read from the planar image of thecross-section from which the obtained single fiber curvature has beenremoved.

Examples of a carbon fiber bundle having a plurality of such singlefibers include, for example, TR50S and TR30L (trade names), manufacturedby Mitsubishi Rayon Co., Ltd.

The above-described single fibers preferably have a ratio of major axisto minor axis (major axis/minor axis) of the cross-section of 1.03 to1.20. If the major axis/minor axis is less than 1.03, adhesion betweenthe single fibers is so strong as a result of the sizing agent aftersizing, which worsens the loosening property of the single fibers whenmixed or impregnated with the resin, whereby on occasion an evenlydispersed molded article cannot be obtained. If the major axis/minoraxis is more than 1.20, the adhesion between single fibers is so weak,and the carbon fiber bundle is easily loosened, whereby on occasionstability during the fixed length cutting step and the morphologicalstability of the carbon fiber bundle after being cut may deteriorate.Especially preferable is 1.05 to 1.15. The above-described majoraxis/minor axis value can be measured as described below.

After passing the carbon fiber bundle to be measured through a tube withthe inner diameter of 1 mm made from a vinyl chloride resin, the carbonfiber bundle is cut with a knife into round slices to be used asspecimens. These specimens are then adhered with their cross-sectionfacing upwards onto a SEM specimen stage, and sputtered with Au to a 10nm thickness. The cross-sections are then observed with a scanningelectron microscope (XL20 (trade name), manufactured by Philips) underthe conditions of an accelerating voltage of 7.00 kV, and operatingdistance of 31 mm, and the major axis and minor axis of the single fibercross-section are then measured.

The above-described single fibers preferably have a Si content of 500ppm or less as measured by ICP emission spectrometry. If the Si contentis more than 500 ppm, the wettability and interfacial adhesion with thematrix resin can deteriorate. Especially preferable is 350 ppm or less.The above-described Si content can be measured as described below.

A carbon fiber bundle is placed in a platinum crucible with a known tareand incinerated in a muffle furnace at from 600 to 700° C. Theincinerated matter is weighed to obtain the ash content. A fixed amountof sodium carbonate is subsequently charged thereto, and the resultingmixture is melted by a burner and is dissolving with DI water(ion-exchange water) to be a constant volume in a 50 ml plasticgraduated flask. The Si content of this sample is then obtained by ICPemission spectrometry.

In the present invention, the carbon fiber bundle has preferably beenpre-sized with a pre-sizing agent consisting of an epoxy resin (I-2).The pre-sizing treatment refers to a treatment for depositing apre-sizing agent onto the carbon fiber bundle. This pre-sizing treatmentallows the convergence of the carbon fiber bundle to be increased, whilesimultaneously also enabling the affinity of the below-describedpre-sizing agents with the carbon fiber bundle to be increased.

A pre-sizing agent consisting of an epoxy resin is preferable because ofits excellent affinity with the single fibers of the carbon fiber bundleand handleability, and also because just a small amount can cause thesingle fibers to converge. In addition, a carbon fiber bundle which hasbeen pre-sized with a pre-sizing agent consisting of an epoxy resinprovides a significantly excellent process passing; for instance thecarbon fiber bundle does not wind onto the roller during the subsequentsizing step. Further, wettability with the sizing agent used in thepresent invention is satisfactory, whereby the sizing agent can beevenly deposited.

When a carbon fiber bundle is pre-sized with a pre-sizing agentconsisting of an epoxy resin, usually, an aqueous pre-sizing agentsolution is used in which a water-soluble or water-dispersible epoxyresin is dissolved or dispersed in water. The water-soluble orwater-dispersible epoxy resin is not particularly restricted, so that aknown resin can be used. If the resin can be used in an aqueoussolution, a modified epoxy resin can also be used. In addition, a singlekind of epoxy resin can be used alone, or 2 or more kinds can be usedmixed together. From the viewpoint of process passing for thebelow-described step for depositing the sizing agent and other factors,it is more preferable that a resin which is liquid at room temperatureand a resin which is solid at room temperature are used in combinationas the epoxy resin.

Examples of water-soluble epoxy resins include resins having glycidylgroups on both ends of a ethylene glycol chain, and resins havingglycidyl groups on both ends of ethylene oxide added on both ends ofbisphenol A, F, S, etc. A compound having an alicyclic epoxy group inplace of the glycidyl group can also be used.

Examples of water-dispersible epoxy resins include bisphenol A typeepoxy resins, bisphenol F type epoxy resins and bisphenol S type epoxyresins, phenol novolak type epoxy resins, cresol novolak type epoxyresins, biphenyl type epoxy resins, naphthalene-skeleton type epoxyresins, aliphatic-based epoxy resins, dicyclopentadiene type epoxyresins (e.g. HP 7200 (trade name) manufactured by Dainippon Ink andChemicals, Incorporated), glycidyl amine type epoxy resins, and DPPnovolak type epoxy resins (e.g. Epikote 157S65 (trade name) manufacturedby Japan Epoxy Resins Co., Ltd.). A compound having an alicyclic epoxygroup in place of the glycidyl group can also be used.

If using a pre-sizing agent consisting of a water-dispersible epoxyresin, it is preferable to conduct the pre-sizing treatment with anaqueous emulsion to which an emulsifier has been further added. Theemulsifier is not particularly restricted, so that anionic, cationic,nonionic or the like emulsifiers can be used. Among these, anionic ornonionic emulsifiers are preferable, as they have good emulsificationproperty, and are low cost. Non-ionic emulsifiers are especiallypreferable, as they do not interfere with pre-sizing agent stability.

Examples of nonionic emulsifiers include polyethylene glycol type(higher alcohol ethylene oxide adducts, alkylphenol ethylene oxideadducts, aliphatic ethylene oxide adducts, polypropylene glycol ethyleneoxide adducts and the like), and polyhydric alcohol type (glycerin fattyacid esters, sorbitol fatty acid esters, fatty acid alkanolamide and thelike). However, the HLB of the nonionic emulsifier is usually 8 to 20.If a nonionic emulsifier is used whose HLB is outside of this range, astable aqueous emulsion may not be attained.

Examples of anionic emulsifiers include carboxylate type (potassiumoleate, sodium oleate and the like), sulfonate type (sodiumdodecylbenzene sulfonate, sodium dioctylsulfosuccinate and the like),and sulfate type (sodium lauryl sulfate and the like). Examples of theneutralizer include potassium hydroxide, sodium hydroxide, magnesiumhydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate,potassium carbonate, potassium bicarbonate, calcium carbonate, calciumbicarbonate, magnesium carbonate, magnesium bicarbonate,monolaurylamine, trimethylamine, dimethyl monoethanolamine,triethanolamine, ethylenediamine, ammonia, and the like. Examples of thereducing agents include sodium sulfite and the like.

Examples of the emulsification method include a method which employs abatch system with a stirrer, a method which employs a ball mill, amethod which employs a shaking apparatus and a method which employs ahigh-shear emulsion machine, such as a Gaulin homogenizer. By settingthe emulsification temperature higher than the softening temperature ofthe pre-sizing agent to be used, an aqueous emulsion can be obtainedwhich has sufficient stability. The time required for emulsification isusually several minutes to 2 hours. After emulsification, an aqueousemulsion can be obtained by cooling to room temperature. While theaqueous emulsion concentration is not particularly limited, the emulsionis diluted with water so as to have the pre-sizing agent concentrationof about 5 to 60 wt %.

For an aqueous emulsion in which a pre-sizing agent is dispersed, othersizing agents (e.g. vinyl acetate resin emulsion, urethane resinemulsion, acrylic resin emulsion or the like), a silane coupling agent,and an antistatic agent can be used in combination as necessary. Inaddition, a lubricant or smoothing agent can also be used in combinationtherewith.

The amount of such a pre-sizing agent deposited is preferably 0.1 to 2.0wt % to the total carbon fiber bundle, and 0.2 to 1.2 is morepreferable. This range is preferable because within such a range thenumber of molecular layers of the pre-sizing agent covering the carbonfiber surface of the carbon fiber bundle is about 1 to 3. If the amountdeposited is more than 2.0 wt %, the pre-sizing agent acts to causebridging between the carbon fibers to cause pseudo-adhesion between thesingle fibers and to constrain movement of single fibers, whereby thecarbon fiber bundle become less spreadable, which can even result in arisk that the uniformity of the carbon fiber bundle is harmed. Further,the permeability of the sizing agent which is deposited in a later stepis interfered with, whereby there is a risk of a deterioration in theproperties as a carbon fiber bundle, such as it becoming more difficultto obtain a uniform carbon fiber bundle. On the other hand, if theamount deposited is less than 0.1 wt %, the effects of depositing thepre-sizing agent are not exhibited, whereby there is a risk that acarbon fiber bundle having excellent process passing, handleability, andaffinity with the sizing agent cannot be obtained.

The pre-sizing treatment can be carried out in the same manner as thatfor the below-described sizing treatment with a sizing agent.

(Sizing Agent Used in the Sizing Treatment)

In the present invention, the carbon fiber bundle is sized with a sizingagent comprising:

a polymer having a main chain formed of carbon-carbon bonds, containingan acid group in at least a part of side chains or at least a part ofmain chain ends, and representing an acid value of 23 to 120 mgKOH/g asmeasured in accordance with ASTM D1386; or

a polymer having a main chain formed of carbon-carbon bonds, containingat least either of an epoxy group and an ester group in at least a partof side chains or at least a part of main chain ends.

The method of sizing treatment according to the present inventioncomprises a step for depositing a sizing agent which comprises theabove-described polymer onto a carbon fiber bundle. As mentioned above,a carbon fiber bundle onto which a sizing agent comprising theabove-described polymer is deposited may be one pre-sized, in which casethe method of sizing treatment comprises a pre-sizing step with apre-sizing agent and a main sizing step with a sizing agent comprisingthe above-described polymer. From this sizing treatment, convergence ofthe carbon fiber bundle can be further increased, and at the same timethe affinity of the carbon fiber bundle with the matrix resin can beincreased.

In particular, examples of preferable sizing agents in the presentinvention include:

(i) A sizing agent comprising at least 35 wt % of an acid modifiedpolypropylene resin (compound a1) having a weight average molecularweight of 45,000 or less, and an acid value of 23 to 120 mgKOH/g asmeasured in accordance with ASTM D1386;

(ii) A sizing agent comprising at least 35 wt % of an acid modifiedpolypropylene resin (compound a2) having a number average molecularweight of 45,000 or less, and an acid value of 23 to 120 mg KOH/g asmeasured in accordance with ASTM D1386, and at least 5 wt % of anolefin-based thermoplastic elastomer resin (compound b);

(iii) A sizing agent comprising at least 40 wt % of a copolymer(compound c) obtained by copolymerizing ethylene or propylene and anepoxy-containing monomer;

(iv) A sizing agent comprising at least 40 wt % of a copolymer (compoundd) obtained by copolymerizing ethylene or propylene, an epoxy-containingmonomer and an acrylic ester; and

(v) A sizing agent comprising at least 40 wt % of copolymer componentsconsisting of the compound c and the compound d.

The acid modified polypropylene resin (compound a1), which is anessential component of the sizing agent represented by theabove-described (i), is the component to act as an efficient couplingagent, which the acidic group in the molecule boost the interaction withthe single fiber surface of the carbon fiber bundle or the pre-sizingagent deposited to the carbon fiber bundle surface when the complex ofthe carbon fiber bundles and polyolefin-based resin or other such matrixresin is formed, while the polypropylene chain in the skeleton causesstrong bonds to form with the matrix resin as a result of the moleculesbeing entangled together. Therefore, the acid modified polypropyleneresin (compound a1) preferably comprises 35 wt % or more of the sizingagent and more preferably 40 wt % or more.

The weight average molecular weight of the acid modified polypropyleneresin (compound a1) is preferably 45,000 or less, more preferably 30,000or less and further preferably 20,000 or less. If the weight averagemolecular weight is more than 45,000, the mobility in the interfacialphase vicinity may be insufficient, and the intermolecular entanglementwith the matrix resin may be lower, whereby interfacial adhesion cannotbe made sufficiently strong. Further, from the viewpoint of the requiredmolecule length for exhibiting coupling effects at the interfacial phaseof a carbon fiber bundle and the resin, weight average molecular weightis preferably 500 or more. Here, the weight average molecular weight ismeasured by GPC.

The acid value as measured in accordance with ASTM D1386 of the acidmodified polypropylene resin (compound a1) is preferably 23 to 120mgKOH/g, more preferably 29 to 90 mgKOH/g, further preferably 35 to 80mgKOH/g and especially preferably 40 to 75 mgKOH/g. If the acid value isless than 23 mgKOH/g, interaction with the single fiber surface of thecarbon fiber bundle or the pre-sizing agent deposited to the carbonfiber bundle surface is low, whereby high interfacial adhesion cannot beobtained. On the other hand, if the acid value is more than 120 mgKOH/g,affinity with the matrix resin, especially with a polyolefin-basedresin, deteriorates, whereby consequently entangling with the moleculesdoes not sufficiently occur, wherein interfacial adhesion cannot be madesufficiently strong.

Specific examples of such an acid modified polypropylene resin (compounda1) include GF-101 (Trade name, aqueous emulsion) manufactured byYoshimura Oil Chemical Co., Ltd., Hostamont AR 503 and AR 504 (tradenames) manufactured by Clariant and the like.

The sizing agent represented by the above-described (i) preferablyfurther comprises at least 5 wt % of an olefin-based thermoplasticelastomer resin (compound b). The olefin-based thermoplastic elastomerresin (compound b) may make the carbon fiber bundle sufficientlyconvergent and drapable. Also, it keeps itself sufficient affinity withthe polyolefin-based resin or other such matrix resin. More preferableis 8 wt % or more. The weight ratio between the acid modifiedpolypropylene resin (compound a1) and the olefin-based thermoplasticelastomer resin (compound b) is preferably 15/1 to 1/1.

The Vicat softening point as measured in accordance with ASTM D1525-70of the olefin-based thermoplastic elastomer resin (compound b) ispreferably 120° C. or less. More preferable is 110° C. or less, andfurther preferable is 90° C. or less. This is because the carbon fiberbundle after it is dried will be satisfactory convergent if theolefin-based thermoplastic elastomer resin (compound b) has beensufficiently softened for during the step evaporating off the water,which are usually conducted at about 140° C., after depositing anaqueous sizing agent solution in which a sizing agent has been dissolvedor dispersed in water.

Specific examples of such an olefin-based thermoplastic elastomer resin(compound b) include GFE-1030 (Trade name, aqueous emulsion)manufactured by Yoshimura Oil Chemical Co., Ltd., TPO-M142, R110E andT310E (trade names) manufactured by Idemitsu Petrochemical Co., Ltd.,and the like.

The acid modified polypropylene resin (compound a2), which is anessential component of the sizing agent represented by theabove-described (ii), is the component to act as an efficient couplingagent, which the acidic group in the molecule boost the interaction withthe single fiber surface of the carbon fiber bundle or the pre-sizingagent deposited to the carbon fiber bundle surface when the complex ofthe carbon fiber bundles and polyolefin-based resin or other such matrixresin is formed, while the polypropylene chain in the skeleton causesstrong bonds to form with the matrix resin as a result of the moleculesbeing entangled together.

The number average molecular weight of the acid modified polypropyleneresin (compound a2) is preferably 45,000 or less, more preferably 30,000or less, further preferably 20,000 or less and especially preferably10,000 or less. If the weight average molecular weight is more than45,000, the mobility in the interfacial phase vicinity may beinsufficient, and the intermolecular entanglement with the matrix resinmay be lower, whereby interfacial adhesion cannot be made sufficientlystrong. Further, from the viewpoint of the required molecule length forexhibiting coupling effects at the interfacial phase of a carbon fiberbundle and the resin, number average molecular weight is preferably 500or more. Here, the number average molecular weight is measured by GPC.

The acid value as measured in accordance with ASTM D1386 of the acidmodified polypropylene resin (compound a2) is preferably 23 to 120mgKOH/g, more preferably 29 to 90 mgKOH/g, and further preferably 35 to80 mgKOH/g. If the acid value is less than 23 mgKOH/g, interaction withthe single fiber surface of the carbon fiber bundle or the pre-sizingagent deposited to the carbon fiber bundle surface is low, whereby highinterfacial adhesion cannot be obtained. On the other hand, if the acidvalue is more than 120 mgKOH/g, affinity with the matrix resin,especially with a polyolefin-based resin, deteriorates, wherebyconsequently entangling with the molecules does not sufficiently occur,wherein interfacial adhesion cannot be made sufficiently strong.

Specific examples of such an acid modified polypropylene resin (compounda2) include GF-101 (Trade name, aqueous emulsion) manufactured byYoshimura Oil Chemical Co., Ltd., Hostamont AR 503 and AR 504 (tradenames) manufactured by Clariant and the like.

The olefin-based thermoplastic elastomer resin (compound b) contained inthe sizing agent represented by the above-described (ii) may make thecarbon fiber bundle sufficiently convergent and drapable. Also, it keepsitself sufficient affinity with the polyolefin-based resin or other suchmatrix resin.

The Vicat softening point as measured in accordance with ASTM D1525-70of the olefin-based thermoplastic elastomer resin (compound b) ispreferably 120° C. or less. More preferable is 110° C. or less, andfurther preferable is 90° C. or less. This is because the carbon fiberbundle after it is dried will be satisfactory convergent if theolefin-based thermoplastic elastomer resin (compound b) has beensufficiently softened for during the step evaporating off the water,which are usually conducted at about 140° C., after depositing anaqueous sizing agent solution in which a sizing agent has been dissolvedor dispersed in water.

Specific examples of such an olefin-based thermoplastic elastomer resin(compound b) include GFE-1030 (Trade name, aqueous emulsion)manufactured by Yoshimura Oil Chemical Co., Ltd., TPO-M142, R110E andT310E (the above are trade names) manufactured by Idemitsu PetrochemicalCo., Ltd. and the like.

The sizing agent represented by the above-described (ii) preferablyfurther comprises 35 wt % or more, preferably 40 wt % or more, of theacid modified polypropylene resin (compound a2), and 5 wt % or more,preferably 8 wt % or more, of the olefin-based thermoplastic elastomerresin (compound b). Since these two compounds take on an important rolein the manner described above, in order to effectively express theirroles their minimum content is respectively independently prescribed.The weight ratio between the acid modified polypropylene resin (compounda1) and the olefin-based thermoplastic elastomer resin (compound b) ispreferably 15/1 to 1/1.

The essential components of the sizing agents represented by theabove-described (iii) to (v), that is a copolymer component consistingof one or both of a copolymer (compound c) obtained by copolymerizingethylene or propylene and an epoxy-containing monomer, and a copolymer(compound d) obtained by copolymerizing ethylene or propylene, anepoxy-containing monomer and an acrylic ester, act extremely efficientlyas a coupling agent between the matrix resin such as a polyolefin-basedresin and the carbon fiber bundle. The reason for this is that since themain skeleton of the polymer is formed from ethylene or propylene units,its compatibility with the matrix resin is very excellent, and further,that since an epoxy group is contained in the molecule, a strongchemical interaction can be formed with the single fiber surface of thecarbon fiber bundle or the pre-sizing agent deposited to the carbonfiber bundle surface. The sizing agent contains these copolymercomponents of preferably 40 wt % or more, more preferably 50 wt % ormore. If less than 40 wt %, the improved performance of interfacialadhesion due to the copolymer components cannot be sufficientlyexhibited in some cases. The copolymer (compound c) obtained bycopolymerizing ethylene or propylene and an epoxy-containing monomer canbe used alone ((iii)). The copolymer (compound d) obtained bycopolymerizing ethylene or propylene, an epoxy-containing monomer and anacrylic ester can be used alone ((iv)). The copolymer (compound c)obtained by copolymerizing ethylene or propylene and an epoxy-containingmonomer and the copolymer (compound d) obtained by copolymerizingethylene or propylene, an epoxy-containing monomer and an acrylic estercan be used together ((v)).

The ratio of units derived from the epoxy-containing monomer in thesecopolymer components, although not particularly limited, is preferably5% or more by mole ratio, and more preferably 10% or more, in order forthe effects of the epoxy group to be expressed. The Vicat softeningpoint of these copolymer components, although not particularly limited,is preferably 120° C. or less, more preferably 110° C. or less, andfurther preferably 90° C. or less. This is, as described above, becausesatisfactory convergence of the carbon fiber bundle after the dryingstep can be conferred.

Examples of such a copolymer (compound c) obtained by copolymerizingethylene or propylene and an epoxy-containing monomer include Bondfast2C and Bondfast E (trade names) manufactured by Sumitomo Chemical Co.,Ltd., Rexpearl RA3150 (trade name) manufactured by Japan PolyolefinCorporation, Sepolsion G118 (trade name) manufactured by Sumitomo SeikaChemicals Co., Ltd., and the like. Examples of a copolymer (compound d)obtained by copolymerizing ethylene or propylene, an epoxy-containingmonomer and an acrylic ester include Bondfast 7L and Bondfast 7M (tradenames) manufactured by Sumitomo Chemical Co., Ltd., and the like.

The sizing agent represented by the above-described (iii) to (v)preferably further comprises a copolymer (compound e) of ethylene orpropylene, an acrylic ester and a monomer containing an acid anhydridegroup. Copolymer (compound e) of ethylene or propylene, an acrylic esterand a monomer containing an acid anhydride group also acts extremelyefficiently as a coupling agent between the matrix resin such as apolyolefin-based resin and the carbon fiber bundle. The reason for thisis that since the main skeleton of the polymer is formed from ethyleneor propylene units, its compatibility with the matrix resin is veryexcellent, and further, that since an acid group is contained in themolecule, a strong chemical interaction can be formed with the singlefiber surface of the carbon fiber bundle or the pre-sizing agentdeposited to the carbon fiber bundle surface. The sizing agent containsthe copolymer (compound e) of ethylene or propylene, an acrylic esterand a monomer containing an acid anhydride group of preferably 40 wt %or more, more preferably 50 wt % or more. If less than 40 wt %, theimproved performance of interfacial adhesion due to this copolymercomponent cannot be sufficiently exhibited in some cases.

The Vicat softening point of the copolymer (compound e) of ethylene orpropylene, an acrylic ester and a monomer containing an acid anhydridegroup, although not particularly limited, is preferably 120° C. or lessand more preferably 110° C. or less. This is, as described above,because satisfactory convergence of the carbon fiber bundle after thedrying step can be conferred.

Specific examples of such a copolymer (compound e) of ethylene orpropylene, an acrylic ester and a monomer containing an acid anhydridegroup include the Bondine (registered trademark) series, manufactured bySumitomo Chemical Co., Ltd., the Rexpearl ET series (trade name)manufactured by Japan Polyolefin Corporation, Sepolsion M220E (tradename) manufactured by Sumitomo Seika Chemicals Co., Ltd., and the like.

The amount of the sizing agent deposited onto a carbon fiber bundle inall these embodiments is not particularly restricted, and may be set asthe amount necessary to express the desired functions from the sizingagent. For example, for a carbon fiber bundle in continuous form, theamount deposited is preferably 0.3 to 5 wt % of the total. Especiallypreferable is 0.8 to 4 wt %. Further, for a carbon fiber bundle cut to aprescribed length, from 1 to 5 wt % is preferable. Especially preferableis 1.2 to 4 wt %. If t there is too little sizing agent, the bundle maybe inadequately convergent and the form stability of the cut bundle maydeteriorate. If there is too much sizing agent, in some caseswettability during the blending step with the resin and the looseningproperty for the single fibers dramatically deteriorate. The amount ofsizing agent deposited onto a carbon fiber bundle is, as the componentamount excluding water of the carbon fiber bundle total, the amount ofthe sizing agent deposited measured by thermal decomposition inaccordance with SACMA method SRM 14-90. When conducting a pre-sizingtreatment, this can be calculated by subtracting the amount of thepre-sizing agent deposited which is separately-measured.

(Sizing Method)

When sizing with an above-described sizing agent, usually, the carbonfiber bundle is sized with an aqueous sizing agent solution in which thesizing agent is dissolved or dispersed in water. Giving consideration toindustrial production, it is preferable in terms of safety and economyto carry out the sizing treatment with an aqueous emulsion in which thesizing agent is dispersed in water. In such a case, a surfactant can beused as an emulsifier for the purpose of evenly dispersing thecomponents in water. The emulsifier at such a stage is not particularlyrestricted, so that anionic, cationic, nonionic or the like emulsifierscan be used. Among these, anionic or nonionic emulsifiers arepreferable, as they have good emulsification property, and are low cost.Further, as is described below, when adding a silane coupling agent intothe aqueous emulsion, nonionic emulsifiers are especially preferable, interms of its stability of the silane coupling agent in the water andalso in terms of the stability of the physical properties of the moldedarticle.

Examples of nonionic emulsifiers include polyethylene glycol type(higher alcohol ethylene oxide adducts, alkylphenol ethylene oxideadducts, aliphatic ethylene oxide adducts, polypropylene glycol ethyleneoxide adducts and the like), and polyhydric alcohol type (glycerin fattyacid esters, sorbitol fatty acid esters, fatty acid alkanolamide and thelike). However, the HLB of the nonionic emulsifier is usually 8 to 20.If a nonionic emulsifier is used whose HLB is outside of this range, astable aqueous emulsion may not be attained.

Examples of anionic emulsifiers include carboxylate type (potassiumoleate, sodium oleate and the like), sulfonate type (sodiumdodecylbenzene sulfonate, sodium dioctylsulfo succinate and the like),and sulfate type (sodium lauryl sulfate and the like). Examples of theneutralizer include potassium hydroxide, sodium hydroxide, magnesiumhydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate,potassium carbonate, potassium bicarbonate, calcium carbonate, calciumbicarbonate, magnesium carbonate, magnesium bicarbonate,monolaurylamine, trimethylamine, dimethyl monoethanolamine, triethanolamine, ethylenediamine, ammonia and the like. Examples of the reducingagents include sodium sulfite and the like.

Examples of the emulsification method include a method which employs abatch provided with a stirrer, a method which employs a ball mill, amethod which employs a shaking apparatus and a method which employs ahigh-shear emulsion machine, such as a Gaulin homogenizer. By settingthe emulsification temperature higher than the softening temperature ofthe sizing agent to be used, an aqueous emulsion can be obtained whichhas sufficient stability. The time required for emulsification isusually several minutes to 2 hours. After emulsification, an aqueousemulsion can be obtained by cooling to room temperature. While theaqueous emulsion concentration is not particularly limited, the emulsionis diluted with water so as to have the sizing agent concentration ofabout 5 to 60 wt %.

For an aqueous emulsion in which a sizing agent is dispersed, othersizing agents (e.g. vinyl acetate resin emulsion, urethane resinemulsion, acrylic resin emulsion, epoxy resin emulsion or the like), asilane coupling agent, and an antistatic agent can be used incombination as necessary. In addition, a lubricant or smoothing agentcan also be used in combination therewith.

Examples of silane coupling agents which can be used include a silanecoupling agent having in the molecule any one of an epoxy group, a vinylgroup, an amino group, a methacrylic group, an acrylic group and astraight chain alkyl group. The silane coupling agent can be employedalone, or two or more kinds thereof can be employed mixed together.Among silane coupling agents, epoxy silanes, amino silanes and straightchain silanes having in the molecule an epoxy group, an amino group or astraight chain alkyl group are particularly preferable. Preferableexamples for a epoxy group contained in the silane coupling agent ofepoxy silanes include glycidyl groups, alicyclic epoxy groups and thelike, and specific examples of the silane coupling agent include A-186,A-187, AZ6137, AZ6165 (trade names) manufactured by Nippon UnicarCompany Limited and the like. Examples of the silane coupling agent ofamino silanes agent include substances having a primary amine, asecondary amine, or both of these, and specific examples include A-1100,A-1110, A-1120, Y-9669, A-1160 (trade names) manufactured by NipponUnicar Company Limited and the like. Examples of straight chain alkylsilanes include substances having a hexyl group, an octyl group or adecyl group and specific examples include AZ6171, AZ-6177 (trade names)manufactured by Nippon. Unicar Company Limited, and KBM-3103C (tradename) manufactured by Shin-Etsu Chemical Co., Ltd. and the like.

The amount of silane coupling agent is preferably 5 wt % or less, morepreferably 4 wt % or less, with respect to 100 wt % of the totalcomponent amount (total solid amount) excluding water of the aqueousemulsion in which the sizing agent is dispersed. If the amount added ismore than 5 wt %, cross-linking of the silane coupling agent proceeds,whereby the carbon fiber bundle become hard and brittle, to be a reasonto form longitudinal cracks and to lower interfacial adhesion.

Examples of a method for sizing with an aqueous sizing agent solutioncontaining a sizing agent such as that described above include a touchroll method which deposits the aqueous sizing agent solution bycontacting the roll with a carbon fiber bundle consisting of singlecarbon fibers after surface transcription by dipping part of a roll inan aqueous sizing agent solution, and a dipping method which controlsthe amount of the aqueous sizing agent solution deposited by directlydipping a carbon fiber bundle consisting of single carbon fibers into anaqueous sizing agent solution and then passing it through a nip roll asnecessary. Between these the touch roll method is preferable. Especiallypreferable in terms of the amount of sizing agent deposited or bundlewidth control is a method wherein a carbon fiber bundle is brought intocontact with a plurality of touch rolls and then the aqueous sizingagent solution is deposited over multiple stages. Subsequently,pre-drying and heat treatment are carried out as necessary. The specificconditions can be selected as appropriate so that the carbon fiberbundles can express the desired properties.

(Sized Carbon Fiber Bundles)

The carbon fiber bundle according to the present invention may be incontinuous form or may be cut to a prescribed length.

The mass per unit length of a carbon fiber bundle cut to a prescribedlength is preferably 0.4 to 15 g/m. A carbon fiber bundle having a massper unit length less than 0.4 g/m is not only economicallydisadvantageous, but also may affect the incorporating process passingof the carbon fiber bundle in the pellet production step. On the otherhand, if greater than 15 g/m, it becomes more difficult to completelycarry out impregnation of the carbon fiber bundles into the aqueoussizing agent solution, and it may be more difficult to produce a carbonfiber bundle having a stable form. More preferable is 0.6 to 10 g/m, andespecially preferable is 0.8 to 8 g/m.

Although the method of cutting the carbon fiber bundle is notparticularly limited, a rotary cutter method is preferable. Further, thecut length (length of the carbon fiber bundles) may be 2 to 30 mm,preferably 4 to 24 mm and more preferably 6 to 20 mm. A rotary cuttermethod allows the cut length to be regulated by adjusting the intervalbetween the teeth of the apparatus being used.

When cutting by a rotary cutter method, if the carbon fiber bundlethickness becomes too thick to result cutting defects, operationimpossibility by winding a carbon fiber bundle around the rotor, andform irregularities after cutting, it is advantageous for the carbonfiber bundle thickness to be thin. In the case of the carbon fiberbundle having a large mass per unit length whose mass per unit length ismore than 1.5 g/m, it is important that the fibers of the carbon fiberbundle are opened up as much as possible so that the aqueous sizingagent solution can be evenly deposited as far as the interior portionsof the carbon fiber bundle. Therefore, it is preferable to transfer in amanner with essentially no twisting of the carbon fiber bundle whilecontrolling so that the carbon fiber bundle width/thickness increasesusing a guide roll, comb guide, spreader bar and the like.

However, if the width of a carbon fiber bundle cut to a prescribedthickness widens, longitudinal cracks form more easily along the fiberorientation direction, whereby maintaining the form tends to be moredifficult during production or when used after being produced. Thistendency is especially pronounced in carbon fiber bundles having a largemass per unit length. Therefore, it is preferable to control thewidth/thickness of the carbon fiber bundle of 3 to 10 by adjusting thewidth of a guide attached to the rotary cutter. If width/thickness is 3or more, the occurrence of miscuts during the cutting process using arotary cutter can be suppressed. If width/thickness is more than 10,although miscuts during cutting are less likely to occur, the thicknessbecomes too thin, whereby it is easier for longitudinal cracks of thecarbon fiber bundle to form after cutting to give rise to the risk thatsubsequent process passing may deteriorate. Further, to cut a carbonfiber bundles having a large mass per unit length thinly and broadly inthe manner of a conventional type, the number of carbon fibers which canbe simultaneously treated decreases, so that to make up for thedecreased amount the cutter width needs to be broadened or the treatmentspeed has to be increased, thereby inviting the risk of increasing theload placed on equipment or decreasing the production efficiency.

This cutting is preferably conducted on a carbon fiber bundle which isin a moist state after the aqueous sizing agent solution has beendeposited to the carbon fiber bundle. This utilizes convergent effectcaused by the surface tension of the aqueous sizing solution andabsorption of impact shearing stress generated during the cutting bysoft state in a moist of to prevent fiber cracking. During the cutting,preferable is a moist state in which the moisture content of a carbonfiber bundle is 20 to 60 wt %, especially 25 to 50 wt %. If the moisturecontent is less than 20 wt %, fiber cracking and fluff are more likelyto occur during cutting. On the other hand, if the moisture content ismore than 60 wt %, water is excessively deposited to the single fibersurface, thereby increasing the risk that single fibers converge in acircle due to the surface tension of the water, thus causing higherincidence of miscuts and blade clogging during cutting. In addition,extra treatments can be carried out prior to cutting using water or anaqueous sizing agent solution to adjust the moisture content, asnecessary.

Examples of a method for drying the carbon fiber bundle after cuttinginclude hot-air drying. If a hot-air drying method is employed, thebundle is preferably dried while it is transferred with vibrating,because not only the moisture evaporation efficiency is improved, butthe carbon fiber bundles can be prevented from adhering together. If thevibration is too vigorously during drying, fiber cracking may occur morereadily, and the ratio of carbon fiber bundles having a width/thicknessof less than 3 may increase. If the vibration is too weak,pseudo-adhesion takes place between the fibers, which leads to a bunchedup form. Accordingly, it is necessary to set to appropriate vibrationconditions. In order to not only eliminate the fragmented carbon fiberbundles, but improve the hot-air flow, it is more preferable to vibrateand dry while transferring on a vibrating mesh. Further, to improvedrying efficiency, auxiliary means, such as infrared emission can alsobe simultaneously used.

(Thermoplastic Resin Composition)

The carbon fiber bundle according to the present invention can be formedinto a thermoplastic resin composition by kneading with a thermoplasticresin as the matrix resin. When kneading a carbon fiber bundle intothermoplastic resin, preferably the carbon fiber bundles are fed into anextruder in a continuous form or a form that has been cut intopredetermined lengths, and then kneaded with the thermoplastic resin toform into pellets. The thermoplastic resin composition according to thepresent invention can also provide an arbitrarily shaped molded article(carbon fiber reinforced composite molded article) by molding inaccordance with a well-known molding method such as injection molding orthe like.

Concerning preparation of the thermoplastic resin composition accordingto the present invention, 3 and 60 wt %, more preferably 5 to 50 wt %,of the carbon fiber bundle according to the present invention preferablyare blended. By blending 3 wt % or more of the carbon fiber bundles, theimproved effect on mechanical properties of the molded article isremarkable. On the other hand, if this exceeds 60 wt %, no furtherremarkable improvement in effects is seen, while the process stabilityduring pellet production may deteriorate and additionally unevenness orthe like may occur in the pellets, whereby there is the risk thatquality stability of the molded article may worsen.

The thermoplastic resin used as the matrix resin in the presentinvention is not particularly restricted, but an polyolefin-based resinis most preferable, due to its affinity with the sizing agent depositedto the single fibers of the carbon fiber bundle. Other examples includeat least one selected from the group consisting of a polycarbonateresin, ABS resin, AS resin, polyoxymethylene resin, nylon resin,polyphenylene sulfide resin, polyether sulfine resin, polyether imideresin, polyester resin and alloy-based resins thereof. Especially whenemploying a polyolefin-based resin as the matrix resin, a small amountof various modified polyolefin-based resins may be added to furtherimprove the mechanical properties.

A molded article obtained by molding the thermoplastic resin accordingto the present invention has excellent mechanical properties, as well asexcellent production efficiency and economic cost. Such a molded articleis suitable for automotive parts, housing parts of a portable electricappliance, housing parts of common home electric appliances and thelike.

EXAMPLES

The present invention will now be explained in further detail withreference to the following Examples. The measurement and evaluation ofthe various properties in the present Examples was conducted inaccordance with the following methods.

(Depth of the Wrinkle on the Surface of Single Fibers of Carbon FiberBundle)

The depth of wrinkles which are present on the surface of single fibersof the carbon fiber bundle according to the present invention wasmeasured from the vertical difference between a highest portion and alowest portion in a region defined by 2 μm of circumferential length×1μm of fiber axial direction length. The vertical difference was measuredbased on a surface shape obtained by scanning the surface of the singlefibers with a scanning atomic force microscope (AFM). Specifically, thiswas as follows.

Several single fibers of a carbon fiber bundle were placed onto aspecimen stage, and fixed at both ends. Dotite was applied around theirperiphery to form measurement samples. Employing a cantilever made fromsilicon nitride, an atomic force microscope (Model: SPI 3700/SPA-300(trade name), manufactured by Seiko Instruments Inc.) was used tomeasure in AFM mode by repeatedly scanning a 2 to 7 μm range in theperiphery direction of the single fibers while slowly moving in 1 μmintervals across the fibers in a fiber axial direction. The lowfrequency component of the obtained measured images was cut bytwo-dimensional Fourier transform, and the cut images then underwent aninverse transform. The vertical difference between the highest portionand the lowest portion in the region defined by 2 μm of circumferentiallength×1 μm of fiber axial direction length was then read and evaluatedfrom the planar image of the cross-section from which the obtainedsingle fiber curvature had been removed.

(Ratio of Major Axis to Minor Axis (Major Axis/Minor Axis) of SingleFiber Cross-Sections in Carbon Fiber Bundle)

After passing the carbon fiber bundle to be measured through a tube withthe inner diameter of 1 mm made from a vinyl chloride resin, the carbonfiber bundle was cut with a knife into round slices to be used asspecimens. These specimens were then adhered with their cross-sectionfacing upwards onto a SEM specimen stage, and sputtered with Au to a 10nm thickness. The cross-sections were then observed with a scanningelectron microscope (XL20 (trade name) manufactured by Philips) underthe conditions of an accelerating voltage of 7.00 kV, and operatingdistance of 31 mm, for evaluation by measuring the major axis and minoraxis of the single fiber cross-sections.

(Strand Strength and Strand Elastic Modulus)

These evaluated in accordance with JIS R7601.

(Amount of Pre-Sizing Agent Deposited)

The amount of the pre-sizing agent deposited on a pre-sized carbon fiberbundle was measured by the Soxhlet extraction method usingmethylethylketone in accordance with JIS R7601.

(Amount of Sizing Agent Deposited)

The amount of the sizing agent deposited on a sized carbon fiber wasmeasured by thermal decomposition in accordance with SACMA method SRM14-90. When the bundle was pre-sized and then sized, the amount of thesizing agent deposited was determined by calculating the increase fromthe amount of pre-sizing agent deposited which is already determinedseparately.

(Moisture Content)

A carbon fiber bundle cut to a prescribed length was dried for hour at110° C. The weight change before and after drying was taken as themoisture content.

(Si Content)

A carbon fiber bundle was placed in a platinum crucible with a knowntare and incinerated in a muffle furnace at 600 to 700° C. Theincinerated matter is weighed to obtain the ash content. A fixed amountof sodium carbonate is subsequently charged thereto, and the resultingmixture is melted by a burner and is dissolved in DI water (ion-exchangewater) to be a constant volume in a 50 ml plastic graduated flask. TheSi amount of this sample is then obtained by ICP emission spectrometry.

(Evaluation of Mechanical Properties of Molded Articles)

Tensile strength at break was evaluated in accordance with JIS K7113,bending strength and elastic modulus were evaluated in accordance withJIS K7203, and Izod strength (⅛″ notch, ⅛″ reverse notch) was evaluatedin accordance with ASTM D256. These measurements were conducted at roomtemperature.

<Carbon Fiber Bundles (Raw Materials)>

The carbon fiber bundles TR50S, TR30L, MR40 and TR40 (trade names,manufactured by Mitsubishi Rayon Co., Ltd.; non-pre-sized products)consisting of 12,000 or 50,000 filaments which use polyacrylic fiber astheir raw material, were employed as the raw materials.

In addition, the carbon fiber bundle (raw material) CF1 was preparedaccording to the following method.

A spinning solution of an acrylonitrile-based polymer dissolved indimethylacetoamide was expelled into a first coagulation bath containingan aqueous dimethylacetoamide solution at a concentration of 50 to 70 wt% and a temperature of 30 to 50° C., to thereby form coagulated fibers.Next, the coagulated fibers were drawn by a fixed length in a secondcoagulation bath containing an aqueous dimethylacetoamide solution at aconcentration of 50 to 70 wt % and a temperature of 30 to 50° C. Theresulting product was wet-heat drawn by 4-fold or more to thereby obtaina carbon fiber precursor fiber bundle. The ratio of the major axis andminor axis of the carbon fiber precursor fiber bundle cross-section andthe depth of the wrinkles formed on the surface can be adjusted bychanging the concentration and temperature of the second coagulationbath, as well as by changing the drawing conditions. A silicon-based oilwas then deposited to maintain the stability of the carbon fiberprecursor fiber bundle.

Subsequently, a plurality of carbon fiber precursor fiber bundles werealigned in parallel and placed into a furnace for flame-proofingtreatment. An oxidizing gas such as air heated to 200 to 300° C. wasblown onto the carbon fiber precursor fiber bundles to flame-proof thecarbon fiber precursor fiber bundles, whereby flame-proofed fiberbundles were obtained. Next, these flame-proofed fiber bundles wereplaced in a carbonizing furnace, and carbonized in an inert atmosphereat a temperature of 1,200 to 1,400° C. To improve the affinity with theresin, a wet electrolytic oxidation treatment was then employed toincorporate an oxygen-containing functional group onto the surfaces,whereby the carbon fiber bundle (raw material) CF1 was produced.

The properties of the above-described carbon fiber bundles (rawmaterials) are shown in Table 1. TABLE 1 Carbon fiber bundle (rawmaterial) TR50S TR30L MR40 TR40 CF1 Depth of the wrinkle (nm) 100 100 1010 100 Major axis/minor axis 1.08 1.08 1.00 1.00 1.08 Mass per unitlength (g/m) 0.80 3.33 0.60 0.83 0.80 Number of single fibers 12,00050,000 12,000 12,000 12,000 Si content (ppm) 300 300 140 140 900 Strandstrength (MPa) 4700 4400 4500 4500 4600 Strand elastic modulus (GPa) 240240 295 235 240<Pre-Sizing Treatment>

The above-described carbon fiber bundles (raw materials) were pre-sizedas necessary with a water-dispersible pre-sizing agent consisting of anepoxy compound, then dried and wound onto a bobbin. A pre-sizing agenthaving the following composition was used adjusting the condition sothat the amount deposited was 0.5 wt %.

(Main Agent)

50 parts by weight of “Epikote 828” (trade name) manufactured by JapanEpoxy Resins Co., Ltd.

30 parts by weight of “Epikote 1001” (trade name) manufactured by JapanEpoxy Resins Co., Ltd.

(Emulsifier)

20 parts by weight of “Pluronic F88” (trade name) manufactured by AsahiDenka Co., Ltd.

<Production of Carbon Fiber Bundles I to XVI>

The carbon fiber bundles (raw materials) shown in Tables 4 and 5 werepassed through a opening bar and a carbon fiber width-regulating baralternatingly by multiple times to set them to a certain carbon fiberwidth, after which they were sized with a given sizing agent. The sizingagents shown in Tables 4 and 5 were used among the sizing agents A to Jwhich were prepared by blending the compounds shown in Table 2 in theratio shown in Table 3. The aqueous emulsions were used where the sizingagent concentration was adjusted as shown in Tables 4 to 6 by regulatingthe water content. The touch roll method described below was employed todeposit the aqueous emulsions.

(Touch Roll Method)

After surface transcription onto the touch roll surface was carried outby dipping part of the touch roll in a bath of the aqueous emulsion, theaqueous emulsion was then deposited by contacting the carbon fiberbundles (raw materials) onto the touch roll. This treatment wasperformed on both the front and back sides by using two touch rolls.

Next, the carbon fiber bundles were cut to a prescribed length (6 mm) byusing a rotary cutter and finally dried by being continuously chargedinto a floor-vibrating hot-air furnace set at 150° C., to thereby yieldcarbon fiber bundles I to XVI.

The employed aqueous emulsions all possessed satisfactory emulsionstability. The carbon fiber bundle throughput and cutting process duringthe sizing treatment were also satisfactory. After drying, no crackswere formed in any of the carbon fiber bundles. The evaluated resultsfor the produced carbon fiber bundles I to XVI are shown in Tables 4 and5. TABLE 2 Product Number Kind (product name) Details Compound a GF-101Acid modified polypropylene (aqueous emulsion containing 10 wt % or lessemulsifier) Number average molecular weight: 4,500 Acid value: 47mgKOH/g Manufactured by Yoshimura Oil Chemical Co., Ltd. Compound bGFE-1030 Olefin-based thermoplastic elastomer (aqueous emulsioncontaining 10 wt % or less emulsifier) Vicat softening temperature: 56°C. Manufactured by Yoshimura Oil Chemical Co., Ltd. Compound c SepolsionCopolymer of ethylene or propylene and an epoxy-containing G118 monomer(main component: ethylene-glycidyl methacrylate copolymer) (aqueousemulsion containing 10 wt % or less emulsifier) Vicat softeningtemperature: 70° C. Manufactured by Sumitomo Seika Chemicals Co., Ltd.Compound d Bondfast Copolymer of ethylene or propylene, anepoxy-containing 7M monomer and an acrylic ester (main component:ethylene-glycidyl methacrylate-methyl acrylate copolymer) (used as anaqueous emulsion adding 20 wt % of an emulsifier*) Vicat softeningtemperature: 25° C. or less Manufactured by Sumitomo Chemical Co., Ltd.Compound e Sepolsion Copolymer of ethylene or propylene, an acrylicester and a M220E monomer containing an acid anhydride group (maincomponent: ethylene-ethyl acrylate-maleic anhydride copolymer) (aqueousemulsion containing 10 wt % or less emulsifier) Vicat softeningtemperature: 60° C. Manufactured by Sumitomo Seika Chemicals Co., Ltd.Others OREVAC Acid modified polypropylene CA100 (used as an aqueousemulsion adding 20 wt % of an emulsifier*) Acid value: 12 mgKOH/gManufactured by Atofina Japan Hydran Urethane-based sizing agent HW-930(aqueous emulsion) Manufactured by Dainippon Ink and Chemicals,Incorporated Epoxy-based Epoxy-based sizing agent sizing agent (aqueousemulsion, EP1001/EP1002/F88 = 40/40/20 (weight ratio)) EP1001, EP1002:bisphenol A diglycidyl ether Manufactured by Japan Epoxy Resins Co.,Ltd. (trade name) F88: Pluronic-type polyether (surfactant) Manufacturedby Asahi Denka Co., Ltd. (trade name) A-187 Epoxy silane coupling agentManufactured by Nippon Unicar Company Limited A-1100 Amino silanecoupling agent Manufactured by Nippon Unicar Company Limited*Pluronic F88 (trade name) manufactured by Asahi Denka Co., Ltd.

TABLE 3 Sizing Agent A B C D E F G H I Compound a GF-101 70 70 70Compound b GFE-1030 27 30 27 47 Compound c Sepolsion 97 60 G118 Compoundd Bondfast 7M 97 Compound e Sepolsion 37 M220E Others OREVAC 50 CA100Hydran 97 HW-930 Epoxy-based 97 sizing agent A-187 3 3 3 3 3 3 3 A-11003The numbers are represent the percentage by weight of each componentexcept the water contained in the respective component.

TABLE 4 Produced carbon fiber bundle I II III IV V VI VII VIII Carbonfiber bundle (raw material) TR50S TR30L TR50S TR50S TR50S TR50S TR50STR40 Pre-sizing treatment No No No No No No No No Sizing Kind A A B C DE F A agent Concentration (wt %) 6.0 6.5 6.0 6.0 6.0 6.0 6.0 5.0 Amountdeposited (wt %) 2.5 2.7 2.5 2.5 2.5 2.5 2.5 2.0 Moisture content (wt %)42 40 42 42 42 42 42 40 Carbon fiber bundle width (mm) 8 20 8 8 8 8 8 8Carbon fiber bundle width/thickness 4 6 4 4 4 4 4 4 presence of cracksNo No No No No No No No

TABLE 5 Produced carbon fiber bundle IX X XI XII XIII XIV XV XVI Carbonfiber bundle (raw material) MR40 CF1 TR50S TR30L TR50S TR50S TR50S TR50SPre-sizing treatment No No Yes Yes Yes No Yes Yes Sizing Kind A A A A BG H I agent Concentration (wt %) 5.0 6.0 6.0 6.5 6.0 6.0 6.0 6.0 Amountdeposited (wt %) 2.0 2.5 2.5 2.7 2.5 2.5 2.5 2.5 Moisture content (wt %)40 42 42 40 42 42 42 42 Carbon fiber bundle width (mm) 6 8 8 20 8 8 8 8Carbon fiber bundle width/thickness 4 4 4 6 4 4 4 4 presence of cracksNo No No No No No No No

Examples 1 to 13 and Comparative Examples 1 to 3

<Production of the Pellets and Molded Articles of the ThermosplasticResin Compostion>

68 parts by weight of a polypropylene resin (EPR co-polymerpolypropylene; trade name: J-5051 HP, manufactured by IdemitsuPetrochemical Co., Ltd.) and 12 parts by weight of a modifiedpolypropylene resin (maleic anhydride co-polymer polypropylene masterbatch P503, manufactured by Mitsubishi Chemical Corporation) werecharged into a twin screw extruder heated to 250° C. 20 parts by weightof the carbon fiber bundles shown in Tables 6 and 7 were charged via aside feeder, and the resulting mixture was kneaded, whereby pellets ofthe thermoplastic resin composition were obtained. In none of theexamples, there were any residue in the twin screw extruder.

The obtained pellets of the thermoplastic resin composition weremanufactured into a molded article by screw inline molder of a 20 mmφand 35 ounce under conditions of a cylinder temperature of 250° C. and adie temperature of 60° C. The mechanical properties of the obtainedmolded articles are shown in Tables 6 and 7. The molded articlesaccording to Examples 1 to 13 were superior to those of ComparativeExamples 1 to 3 in tensile strength at break, bending strength and Izodstrength. It was thereby learned that the carbon fiber bundle accordingto the present invention possessed satisfactory interfacial adhesion.TABLE 6 Example 1 2 3 4 5 6 7 8 Carbon Fiber Bundle I II III IV V VI VIIVIII Tensile Strength at Break (MPa) 110 100 95 95 95 105 100 80 BendingStrength (MPa) 150 140 135 135 134 145 140 115 Bending elastic modulus(MPa) 7500 7400 7300 7400 7300 7400 7400 7200 Izod Strength (⅛″ notch)(J/m) 80 75 75 72 70 85 75 70 Izod Strength (⅛″ reverse notch) (J/m) 240230 230 220 220 250 240 200

TABLE 7 Example Comp. Example 9 10 11 12 13 1 2 3 Carbon Fiber Bundle IXX XI XII XIII XIV XV XVI Tensile Strength at Break (MPa) 75 90 135 125120 67 65 57 Bending Strength (MPa) 110 125 175 170 165 97 94 80 Bendingelastic modulus (MPa) 8400 7200 7500 7400 7400 6800 6800 6300 IzodStrength (⅛″ notch) (J/m) 70 70 85 80 85 67 65 45 Izod Strength (⅛″reverse notch) (J/m) 190 210 270 270 260 190 180 110

Examples 14 and 15, and Comparative Example 4

<Production of the Pellets and Molded Articles of the ThermoplasticResin Composition>

80 parts by weight of a polypropylene resin (EPR co-polymerpolypropylene; trade name: J-5051 HP, manufactured by IdemitsuPetrochemical Co., Ltd.) were charged into a twin screw extruder heatedto 250° C. 20 parts by weight of the carbon fiber bundles shown in Table8 were charged via a side feeder, and the resulting mixture was kneaded,whereby pellets of the thermoplastic resin composition were obtained. Innone of the examples, there were any residue in the twin screw extruder.

The obtained pellets of the thermoplastic resin composition weremanufactured into a molded article by screw inline molder of a 20 mmφand 35 ounce under conditions of a cylinder temperature of 250° C. and adie temperature of 60° C. The mechanical properties of the obtainedmolded articles are shown in Table 8. The molded articles according toExamples 14 and 15 were superior to the molded article of ComparativeExample 4 in tensile strength at break, bending strength and Izodstrength. It was thereby learned that the carbon fiber bundle accordingto the present invention possessed satisfactory interfacial adhesion.TABLE 8 Example Comp. Example 14 15 4 Carbon Fiber Bundle XI I XVITensile Strength at Break (MPa) 90 70 40 Bending Strength (MPa) 105 9056 Bending elastic modulus (MPa) 7300 7300 5100 Izod Strength (⅛″ notch)(J/m) 80 70 50 Izod Strength (⅛″ reverse notch) (J/m) 140 110 90

INDUSTRIAL APPLICABILITY

The carbon fiber bundle according to the present invention is suitablefor making into a thermoplastic resin composition by kneading with athermoplastic resin serving as a matrix resin. Further, by molding sucha thermoplastic resin composition, the present invention is suitable formaking into a molded article (carbon fiber reinforced composite moldedarticle). Such a molded article has excellent mechanical properties, andis also superior in terms of production efficiency and economic cost,and is thus suitable for automotive parts, housing parts of a portableelectric appliances, housing parts of common home electric appliancesand the like.

1. A carbon fiber bundle comprising a plurality of single fibers, andsized with a sizing agent comprising: a polymer having a main chainformed of carbon-carbon bonds, containing an acid group in at least apart of side chains or at least a part of main chain ends, andrepresenting an acid value of 23 to 120 mgKOH/g as measured inaccordance with ASTM D1386; or a polymer having a main chain formed ofcarbon-carbon bonds, and containing at least either of an epoxy groupand an ester group in at least a part of side chains or at least a partof main chain ends.
 2. The carbon fiber bundle according to claim 1,wherein the sizing was conducted after pre-sized with a pre-sizing agentconsisting of an epoxy resin.
 3. The carbon fiber bundle according toclaim 2, wherein the sizing agent comprises at least 35 wt % of an acidmodified polypropylene resin (compound a1) having a weight averagemolecular weight of 45,000 or less and an acid value of 23 to 120mgKOH/g as measured in accordance with ASTM D1386.
 4. The carbon fiberbundle according to claim 3, wherein the sizing agent comprises at least5 wt % of an olefin-based thermoplastic elastomer resin (compound b). 5.The carbon fiber bundle according to claim 4, wherein the compound b hasa Vicat softening point of 120° C. or less as measured in accordancewith ASTM D1525-70.
 6. The carbon fiber bundle according to claim 1,wherein the compound a1 has a weight average molecular weight of 20,000or less, and an acid value of 40 to 75 mgKOH/g as measured in accordancewith ASTM D1386.
 7. The carbon fiber bundle according to claim 2,wherein the sizing agent comprises at least 40 wt % of a copolymer(compound c) obtained by copolymerizing ethylene or propylene and anepoxy-containing monomer.
 8. The carbon fiber bundle according to claim1, wherein the single fibers comprise a plurality of wrinkles on theirsurface, wherein a vertical difference between a highest portion and alowest portion in a region defined by 2 μm of circumferential length×1μm of fiber axial direction length of the single fibers is 40 nm ormore.
 9. The carbon fiber bundle according to claim 1, wherein thesizing agent comprises no more than 5 wt % of a silane coupling agenthaving in the molecule any one of an epoxy group, a vinyl group, anamino group, a methacrylic group, an acrylic group and a straight chainalkyl group in its molecule.
 10. The carbon fiber bundle according toclaim 1, cut to a prescribed length, wherein an amount of the sizingagent deposited to the total is 1 to 5 wt %.
 11. The carbon fiber bundleaccording to claim 10, having a mass per unit length of 0.4 to 15 g/m,and a width/thickness of 3 to
 10. 12. A method for producing a carbonfiber bundle comprising a plurality of single fibers, comprising thesteps of: pre-sizing the carbon fiber bundle with a pre-sizing agentconsisting of an epoxy resin; sizing the pre-sized carbon fiber bundle,so that an amount of a sizing agent to the total is 1 to 5 wt %, byusing an aqueous sizing agent solution dissolving or dispersing in waterthe sizing agent comprising: a polymer having a main chain formed ofcarbon-carbon bonds, containing an acid group in at least a part of sidechains or at least a part of main chain ends, and representing an acidvalue of 23 to 120 mgKOH/g as measured in accordance with ASTM D1386; ora polymer having a main chain formed of carbon-carbon bonds, containingat least either of an epoxy group and an ester group in at least a partof side chains or at least a part of main chain ends; cutting the carbonfiber bundle to a prescribed length; and drying the carbon fiber bundlecut to the prescribed length.
 13. A thermoplastic resin compositioncomprising a thermoplastic resin and the carbon fiber bundle accordingto claim 2, wherein the carbon fiber bundle content is 3 to 60 wt %. 14.The thermoplastic resin composition according to claim 13, wherein thethermoplastic resin is a polyolefin-based resin.
 15. A molded articleobtained by molding the thermoplastic resin composition according toclaim
 14. 16. The carbon fiber bundle according to claim 1, wherein thesingle fibers comprise a plurality of wrinkles on their surface, whereina vertical difference between a highest portion and a lowest portion ina region defined by 2 μm of circumferential length×1 μm of fiber axialdirection length of the single fibers is 40 nm or more.
 17. The carbonfiber bundle according to claim 16, wherein the sizing agent comprises:at least 35 wt % of an acid modified polypropylene resin (compound a2)having a number average molecular weight of 45,000 or less and an acidvalue of 23 to 120 mgKOH/g as measured in accordance with ASTM D1386;and at least 5 wt % of an olefin-based thermoplastic elastomer resin(compound b).
 18. The carbon fiber bundle according to claim 17, whereinthe compound b has a Vicat softening point of 120° C. or less asmeasured in accordance with ASTM D1525-70.
 19. The carbon fiber bundleaccording to claim 16, wherein the sizing agent comprises at least 40 wt% of a copolymer component consisting of one or both of: a copolymer(compound c) obtained by copolymerizing ethylene or propylene and anepoxy-containing monomer; and a copolymer (compound d) obtained bycopolymerizing ethylene or propylene, an epoxy-containing monomer and anacrylic ester.
 20. The carbon fiber bundle according to claim 19,wherein the sizing agent further comprises a copolymer (compound e)obtained by copolymerizing ethylene or propylene, an acrylic ester and amonomer containing an acid anhydride group.
 21. The carbon fiber bundleaccording to claim 16, wherein cross-section of the single fiber have aratio of major axis to minor axis of 1.03 to 1.20, and a Si content of500 ppm or less as measured by ICP emission spectrometry.
 22. The carbonfiber bundle according to claim 19, wherein the sizing agent comprisesno more than 5 wt % of a silane coupling agent having in the moleculeany one of an epoxy group, a vinyl group, an amino group, a methacrylicgroup, an acrylic group and a straight chain alkyl group.
 23. The carbonfiber bundle according to claim 19, cut to a prescribed length, whereinan amount of the sizing agent deposited to the total is 1 to 5 wt %. 24.The carbon fiber bundle according to claim 23, having a mass per unitlength of 0.4 to 15 g/m, and a width/thickness of 3 to
 10. 25. A methodfor producing a carbon fiber bundle comprising a plurality of singlefibers, wherein the single fibers comprise a plurality of wrinkles ontheir surface, wherein a vertical difference between a highest portionand a lowest portion in a region defined by 2 μm of circumferentiallength×1 μm of fiber axial direction length of the single fibers is 40nm or more, comprising the steps of: sizing the carbon fiber bundle, sothat an amount of a sizing agent to the total is 1 to 5 wt %, by usingan aqueous sizing agent solution dissolving or dispersing in water thesizing agent comprising: a polymer having a main chain formed ofcarbon-carbon bonds, containing an acid group in at least a part of sidechains or at least a part of main chain ends, and representing an acidvalue of 23 to 120 mgKOH/g as measured in accordance with ASTM D1386; ora polymer having a main chain formed of carbon-carbon bonds, containingat least either of an epoxy group and an ester group in at least a partof side chains or at least a part of main chain ends; cutting the carbonfiber bundle to a prescribed length with regulating the moisture contentof the carbon fiber bundle to 20 to 60 wt %; and drying the carbon fiberbundle cut to a prescribed length.
 26. A thermoplastic resin compositioncomprising a thermoplastic resin and the carbon fiber bundle accordingto claim 2, wherein the carbon fiber bundle content is 3 to 60 wt %. 27.The thermoplastic resin composition according to claim 26, wherein thethermoplastic resin is at least one selected from the group consistingof polyolefin-based resin, polycarbonate resin, ABS resin, AS resin,polyoxymethylene resin, nylon resin, polyphenylene sulfide resin,polyether sulfine resin, polyether imide resin, polyester resin andalloy-based resins thereof.
 28. A molded article obtained by molding thethermoplastic resin composition according to claim 27.